The instant invention relates to a self-centering drill. More particularly, a self-centering drill having a modified flat bottom section chamfered at its outside edges and having a helical crown with a helical crown point tip, thus, forming six cutting lips. Such a drill is believed to generate smooth surface holes with excellent precision and accuracy, while substantially reducing chatter and vibration, and reducing the frequency of sharpening.
Artisans ranging from the homeowner who dabbles at fix-it projects on the weekend to professional manufacturing operations need to drill holes into various materials, for example, to allow space for a fastener such as a bolt, or to allow for the passage of a gas, a liquid, or light. Many difficulties are encountered during drilling, especially when many holes must be drilled, and especially when they must be drilled at a high rate. For example, many conventional drills leave undesirable rough surfaces or edges in the drilled material, particularly when they lose center. Chatter and vibration of the drill may result in unevenly drilled holes. Some drills are designed to cut through only specific types of materials, and are not suitable for drilling through multi-layered or laminated materials that contain different components in the layers. Oftentimes, resin in wood when heated will cause wood chips to cling to the body of a drill, where those chips then retain even more heat and ruin the drill after just a few holes are completed. Some drills that do not cut cleanly produce undesirable burrs and either tear or splinter the material being drilled into.
The art is replete with drills; however, there exists a need for a drill that better addresses the difficulties encountered by the drilling artisan. A series of drills, commonly known as BULLET(trademark) drills have been marketed. Versions of these bits are disclosed in U.S. Pat. No. 4,968,193, issued Nov. 6, 1990, to Chaconas et al., and U.S. Pat. No. 5,288,183, issued Feb. 22, 1994, to Chaconas et al., and U.S. Pat. No. 6,050,754, issued Apr. 18, 2000, to Thomas, all of which are assigned to Black and Decker, Inc. However, a need exists for more stable drills which can better maintain center and will drill without having to repetitively retract and reinsert the drill, and for drills with greater longevity, and with a reduced tendency to produce a disc in multi-layered or laminated materials.
Others have attempted to design self-centering drills, such as the ones disclosed in U.S. Pat. No. 5,423,640, issued Jun. 13, 1995, to Lindblom, et al., assigned to Sandvik AB, and U.S. Pat. No. 5,758,997, issued Jun. 2, 1998, to Mealey, et al., and U.S. Pat. No. 6,050,754, issued Apr. 18, 2000, to Thomas, assigned to Black and Decker, Inc., and U.S. Pat. No. 5,452,971, issued Sep. 26, 1995, to Nevills, and U.S. Pat. No. 5,442,979, issued Aug. 22, 1995, to Hsu, assigned to Greenfield, Industries, Inc. However, a need still exists for better self-centering drills which can better provide stability while substantially reducing chatter and vibration, while furthermore, being able to cut through a variety of materials, including different material layers laminated into a single product, and which still further, allows for the easy removal of chips during drilling and allows heat to dissipate, and yet still further, reduces the frequency of sharpening.
Applicant has found, surprisingly, that the above mentioned difficulties can be remedied with a self-centering drill having a modified flat bottom section chamfered at is outside edges and having a helical crown with a helical crown point tip, which thus, forms six cutting lips. This point geometry provides for improved cutting action that generates superior surface finishes with excellent drilling precision and accuracy. The design also provides for excellent stability while substantially reducing chatter and vibration. The drill is suitable for cutting through a variety of materials, even when different materials are laminated. And unlike other self-centering drills known in the art, the drill of the present invention consistently produces precisely rounded and uniform holes with no metal burr breakthrough or wood grain tears and splinters. Furthermore, the drill is able to stay sharp after many cuttings.
The present invention relates to a self-centering drill comprising: (a) a shank, a body, and a cutting end, all formed integrally in the drill; (b) the body interposed between the shank and the cutting end, the body having a pair of helical flutes and a corresponding pair of helical lands; (c) the cutting end including a substantially flat bottom section having primary cutting lips which are relief ground, the primary cutting lips forming a primary point angle, and a helical crown having a helical crown point tip that extends from the bottom section, the helical crown point tip having self-centering cutting lips; (d) wherein the outside edges of the bottom section are chamfered to form secondary cutting lips which are radially relieved, the secondary cutting lips forming a secondary point angle; (e) the primary point angle being greater than the secondary point angle. The invention further relates to methods of general drilling and counterbore drilling using the self-centering drills described above.